Sonophotocatalytic Degradation Research Articles

Precursor effects on the physical, biological, and catalytic properties of Fagonia indica Burm.f. mediated zinc oxide nanoparticles.

We report a facile, green and precursor-based comparative study on the biosynthesis of zinc oxide (ZnO) nanoparticles (NPs) using anticancerous Fagonia indica as effective chelating agent. Biosynthesis was carried out using zinc sulfate and zinc acetate as precursor salts to make ZnOS and ZnOA NPs under similar experimental conditions which were characterized extensively for physical and biological properties. Scherrer equation deduced a mean crystallite size of ~23.4 nm for ZnOA NPs and ~41 nm for ZnOS NPs. The nature of the NPs was compared using UV, diffuse reflectance spectra, Fourier transform infrared spectroscopy, thermogravimetric analysis-DTA, selected area electron diffraction, EDS, zeta potential, high resolution (HR)-SEM, and HR-TEM. Detailed in vitro pharmacognostic activities revealed a significant therapeutic potential for ZnOA and ZnOS . Potential antimicrobial activities for the NPs and their nanocosmeceutical formulations are reported. ZnOA NPs were more cytotoxic to Leishmania tropica as compared to ZnOS . Significant antioxidant and protein kinase inhibition was obtained. The hemolytic assay indicated a hemocompatible nature of both ZnOA and ZnOS NPs. Catalytic degradation of crystal violet dye (CVD) by NPs was examined under different parameters (light, dark, UV). Furthermore, sonophotocatalytic degradation of CVD was also studied. Our results suggested that precursor can have a significant effect on the physical, biological, and catalytic properties of the NPs. In future, we recommend different other in vitro, in vivo biological activities, and mechanistic studies of these as-synthesized NPs.

Instantaneous Sonophotocatalytic Degradation of Tetracycline over NU-1000@ZnIn2S4 Core-Shell Nanorods as a Robust and Eco-friendly Catalyst.

The universal pollution of diverse water bodies and declined water quality represent very important environmental problems. The development of new and efficient photocatalytic water treatment systems based on the Z-scheme mechanisms can contribute to tackling such problems. This study reports the preparation, full characterization, and detailed sonophotocatalytic activity of a new series of hybrid NU@ZIS nanocomposites, which comprise a p-n heterojunction of 3D Zr(IV) metal-organic framework nanorods (NU-1000) and photoactive ZnIn2S4 (ZIS) nanostars. Among the obtained materials with varying content of ZIS (5, 10, 20, and 30%) on the surface of NU-1000, the NU@ZIS20 nanocomposite revealed an ultrahigh catalytic performance and recyclability in a quick visible-light-induced degradation of the tetracycline antibiotic in water under sonophotocatalytic conditions. Moreover, increased activity of NU@ZIS20 can be ascribed to the formation of a p-n heterojunction between NU-1000 and ZIS, and a synergistic effect of these components, leading to a high level of radical production, facilitating a Z-scheme charge carrier transfer and reducing the recombination of charge carriers. The radical trapping tests revealed that •OH, •O2-, and h+ are the major active species in the sonophotocatalytic degradation of tetracycline. Possible mechanism and mineralization pathways were introduced. Cytotoxicity of NU@ZIS20 and aquatic toxicity of water samples after tetracycline degradation were also assessed, showing good biocompatibility of the catalyst and efficacy of sonophotocatalytic protocols to produce water that does not affect the growth of bacteria. Finally, the obtained nanocomposites and developed photocatalytic processes can represent an interesting approach toward diverse environmental applications in water remediation and the elimination of other types of organic pollutants.

Hydrogen peroxide enhanced sonophotocatalytic degradation of acid orange 7 in aqueous solution: optimization by Box–Behnken design

AbstractBACKGROUNDSonophotocatalysis has gained great attention for research into practical applications to treat refractory organic dye from wastewater. However, its degradation efficiency needs to be improved further. To further enhance the sonophotocatalytic performance, here we report a novel hydrogen peroxide (H2O2)‐assisted titania (TiO2)‐based sonophotocatalyic system (H2O2‐US‐UV/TiO2) for degradation of acid orange 7 (AO7).RESULTSEffects of operating parameters including catalyst dosage, concentration of the oxidative agents and initial pH were analyzed through a response surface method coupled with Box–Behnken experimental design (RSM‐BBD) and experiments. Introducing H2O2 into the US‐UV/TiO2 system can significantly enhance AO7 removal. A quadratic model was proposed for predicting AO7 degradation using the RSM‐BBD method, and the statistical significance of the model was confirmed by ANOVA. The real AO7 removal efficiency (95.8%) under experimental conditions of 0.5 g L−1 TiO2, 4 mmol L–1 H2O2, and initial pH 3 was comparable with the predicated value (98.6%) obtained from this model. Quenching tests revealed that the hydroxyl radical (˙OH) was the key reactive species in the sonophotocatalytic system. Degradation products including 2‐naphthol, 4‐carboxylphenylglycine, cinnamic acid and 1,10‐Decanediol were identified.CONCLUSIONAdding H2O2 improved the degradation performance of AO7 in the US‐UV/TiO2 system; H2O2 concentration was a more significant experimental factor than initial pH and TiO2 dosage. A degradation pathway of AO7 removal was suggested according to results of liquid chromatography‐mass spectrometry. The novel hybrid H2O2‐US‐UV/TiO2 system can be utilized as an efficient process for recalcitrant dye wastewater treatment. © 2021 Society of Chemical Industry (SCI).

МІКРО- І НАНОСТРУКТУРОВАНИЙ ТИТАНУ(IV) ОКСИД У СОНО-, ФОТО- І СОНОФОТОКАТАЛІТИЧНІЙ ДЕГРАДАЦІЇ КСАНТЕНОВОГО БАРВНИКА РОДАМІНУ Б (ОГЛЯД)

Adsorption methods for removing Rhodamine B from wastewater and oxidative degradation methods based on the use of advanced oxidation processes (sonolysis, photolysis, sono-, photo- and sonophotocatalysis) are considered. It was established that naturally occurring materials (such as clays, zeolites, coal ash, anaerobic sludge, agricultural solid wastes) and their modified or activated analogues are used as adsorbents for the removal of Rhodamine B. The possible mechanism of photo- and sonophotocatalytic degradation of Rhodamine B in the presence of micro- and nanostructured titanium (IV) oxide is presented. The effectiveness of its application for degradation of Rhodamine B is analyzed.

Piezo-enhanced photocatalytic diclofenac mineralization over ZnO

The degradation of diclofenac has been realized for the first time by a piezo-enhanced sonophotocatalytic approach based on ZnO. The sonophotocatalytic degradation showed a slight enhancement in the degradation of the parent compound, whereas strong synergistic effects were observed for the mineralization process when suitable ZnO morphologies are used, reaching 70% of complete degradation of 25 ppm diclofenac using 0.1 g/L ZnO in 360 min. Tests in a complex water matrix show enhanced diclofenac removal, outperforming a TiO2 benchmark photocatalyst. These promising experimental results promote this process as a good alternative to traditional degradation approaches for remediation of real water matrices.

Development of sonophotocatalytic process for degradation of acid orange 7 dye by using titanium dioxide nanoparticles/graphene oxide nanocomposite as a catalyst

In the present study, the sonophotocatalytic degradation of acid orange 7 (AO7) dye was evaluated. The catalyst used was the titanium dioxide nanoparticles/graphene oxide (TiO2/GO) nanocomposite, which was synthesized using the Hummers and Hoffman's method and the liquid phase deposition method. TiO2/GO nanocomposite was characterized through the analyses of transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy Dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. In addition, properties of the surface area and pore size were determined by N2 adsorption–desorption and the Barrett-Joyner-Halenda methods. After modification, the nanocomposite properties showed successful stabilization of TiO2 on the graphene substrate and reduction of the recombinant carrier loads. By utilizing the proposed treatment, complete degradation of AO7 could be achieved under optimal operating parameters (pH = 5, initial concentration of AO7 dye = 50 mg/L, TiO2/GO nanocomposite dose = 0.5 g/L, UV light intensity = 36 W, ultrasonic wave intensity = 35 kHz, and reaction time = 30 min). Scavenging experiments confirmed that OH and h+ radicals were the predominant species in the sonophotocatalytic degradation reactions of the AO7 dye. The stability study confirmed the excellent shelf life of the TiO2/GO nanocomposite, with only a slight reduction in the degradation efficiency of the AO7 dye (<8.27%) detected, after six consecutive cycles of the sonophotocatalytic process. Studies related to the degradability of the AO7 dye and the biodegradability of the effluent from the process showed that the applied sonophotocatalytic system was able to remove the TOC concentration by 83% after a reaction time of 30 min. Moreover, the increase in the BOD5/COD ratio was also a confirmation for the increase in biodegradability of the treated AO7 dye effluent. Finally, the toxicity test showed that the growth inhibition rate of Escherichia coli (E. coli), as a viability index, decreased to about 7.34% after a reaction time of 180 min. This result indicated the formation of compounds with low toxicity and molecular weight over the reaction time of the sonophotocatalytic process of AO7 dye.

Preparation of MgTi2O5 nanoparticles for sonophotocatalytic degradation of triphenylmethane dyes

MgTi2O5 (magnesium dititanate) nanoparticles were prepared by a simple hydrothermal assisted post-annealing method and characterized with various analytical techniques. The catalytic properties (sonocatalytic, photocatalytic and sonophotocatalytic activity) were evaluated using the degradation of triphenylmethane dyes (crystal violet, basic fuchsin, and acid fuchsin). The sonophotocatalytic activity of MgTi2O5 nanoparticles towards crystal violet was found to be ~2.9 times higher than the photocatalytic activity and ~20 times higher than that of the sonocatalytic processes. In addition, the sonophotocatalytic efficiency of MgTi2O5 nanoparticles was found to be remarkable for the degradation of basic fuchsin (cationic dye) and acid fuchsin (anionic dye). The mechanism of these catalytic activities has been discussed in detail.

Synthesis and characterization of chitosan-supported Fe2O3 nanohybrids for rapid sonophotocatalytic degradation of 2,4,6-trichlorophenol.

The present study reports the design of heterogeneous photocatalytic system using Fe2O3 with chitosan (CS) as a matrix for the sonophotocatalytic degradation of 2,4,6-trichlorophenol (2,4,6-TCP). CS was chosen as a polymer matrix as it is abundant in nature, eco-friendly, and can be easily processed into microparticles, nanofibers, as well as nanoparticles and shows the tendency of adhesion towards a vast range of solid substrates besides serving as a chelating agent toward metallic oxides. The nanohybrids were characterized via Fourier transformation infrared spectrum (FT-IR), X-ray diffraction (XRD), scanning electron microscopy coupled with electron dispersive spectrum (SEM-EDS), thermogravimetric analysis (TGA), and UV-visible diffuse reflectance (UV-Vis-DRS) analyses. Infrared spectroscopy (IR) studies confirmed synergistic interaction between Fe2O3 and CS. The XRD measurements confirmed the crystalline morphology while SEM revealed formation of rod-like structures. The TGA studies confirmed higher thermal stability of CS/Fe2O3 as compared to pure CS. The optical band gap for CS and CS/Fe2O3 was calculated to be 3 eV and 2.25 eV, respectively, from diffuse reflectance spectral (DRS) studies. Rapid photocatalytic degradation of 2,4,6-TCP was observed under UV light irradiation in presence of CS and CS/Fe2O3 nanohybrids which revealed 83.19% and 95.20% degradation within a short span of 60 min. The degraded fragments were identified using liquid chromatography-mass spectrometry (LC-MS). The present study on the development of ecofriendly nanohybrid photocatalyst is expected to provide experimental basis for the future development of CS-based photocatalysts which can be easily processed into membranes/filters for the industrial scale degradation of toxic organic pollutants.

Rational construction of CeO2–ZrO2@MoS2 hybrid nanoflowers for enhanced sonophotocatalytic degradation of naproxen: Mechanisms and degradation pathways

This study proposed a novel heterogeneous sonophotocatalytic system to effectively treat pharmaceutical wastewater employing molybdenum disulfide (MoS2) decorated ceria (CeO2)-zirconia (ZrO2) ternary hybrid nanoflowers (CZx/100 M). The generation of dominant oxidizing species, both radical and nonradical, was deeply scrutinized under ultrasound (US) irradiation coupled with visible-light by electron spin resonance spectroscopy analysis and scavenging experiments, for the first time. Interestingly, the pairing of US with visible-light illumination in a sonophotocatalytic degradation system resulted in 96% degradation efficiency of naproxen (NPX) within 40 min, which confirmed that excellent synergistic effect of sono- and photocatalytic mechanisms in the presence of 0.5 g/L sonophotocatalyst at pH 5.8. The sonophotocatalytic activity was also manifested at various reaction time, catalyst dose, solution pH, initial NPX concentrations, and US frequency and power and in the presence of various anions. The mechanism for the catalytic degradation of NPX is proposed in the US/Vis/CZx/100 M system, and transformation products formed during the process were identified by an ultra-high performance liquid chromatography-mass spectrometry technique.

Microwave-assisted fabrication of ZnO/MK10 nanocomposite: an efficient photocatalytic and sonophotocatalytic degradation of methylene blue dye

In this research, we have designed a microwave-assisted procedure for processing of ZnO nanoparticles (ZnO NPs) modified by Montmorillonite K10 (MK10) nanosheets in a one-pot strategy using Carrisa edulis fruit extract as the capping agent. The sample was characterized with X-ray diffraction, infrared, ultraviolet–visible spectroscopy, transmission electron microscopy, X-ray diffraction, atomic force microscopy, zeta potential, and photoluminescence. We observed that the ZnO/MK10 nanocomposite exhibited superior photocatalytic ability toward methylene dye (MB) degradation. ZnO/MK10 nanocomposite shows excellent sonophotocatalytic effect, which is three times higher than that of MB photocatalytic effect. This nanocomposite has been further active in trapping species, potential mechanism for sonophotocatalytic degradation, excellent recyclability, and stability.

Understanding the origin of synergistic catalytic activities for ZnO based sonophotocatalytic degradation of methyl orange

Many studies have documented the existence of synergistic catalytic activities for ZnO based sonophotocatalysis, but the role of ultrasonic field during this sonophotocatalytic process is still unclear. In this work, ZnO samples with three different morphologies (rod-like, flower-like and sheet-like) have been synthesized for the sonophotocatalytic degradation of methyl orange (MO). The results indicate that MO degradation efficiency of ZnO based sonophotocatalysis is found to be higher than the sum of ZnO based photocalysis and sonocatalysis, which indicates the existence of synergy in the ZnO based sonophotocatalytic degradation of MO. The mechanistic investigation indicates that reactive oxygen species can be produced by ZnO in the presence of ultrasound. In addition, the presence of ultrasound in the ZnO based sonophotocatalysis is beneficial for the separation of electron-hole pairs of ZnO based photocatalysis, leading to the production of more reactive oxygen species in the ZnO based sonophotocatalysis. Overall, the origin of synergistic catalytic activities for ZnO based sonophotocatalytic degradation of MO has been revealed in this study.

Sonophotocatalytic Degradation of Malachite Green by Nanocrystalline Chitosan-Ascorbic Acid@NiFe2O4 Spinel Ferrite

Statistics show that more than 700 thousand tons of dye are produced annually across the globe. Around 10–20% of this is used in industrial processes such as printing and dyeing, while about 50% of the dye produced is discharged into the environment without proper physicochemical treatment. Even trace amounts of dye in water can reduce oxygen solubility and have carcinogenic, mutagenic, and toxic effects on aquatic organisms. Therefore, before dye-containing wastewater is discharged into the environment, it must be properly treated. The present study investigates the green synthesis of nickel ferrite NiFe2O4 (NIFE) spinel magnetic nanoparticles (MNPs) via chemical coprecipitation of a solution of Ni2+/Fe3+ in the presence of a biopolymer blend of chitosan (CT) and ascorbic acid (AS). The magnetic nanomaterial was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy–energy dispersive X-ray analysis (SEM-EDX), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), differential scanning calorimetry (DSC), and vibrating-sample magnetometry (VSM). The material was further explored as a catalyst for the photocatalytic degradation of malachite green (MG) under visible light irradiation coupled with ultrasonic waves. The combination of 90 min of visible solar light irradiation with 6.35 W·mL−1 ultrasonic power at pH 8 resulted in 99% of the photocatalytic efficiency of chitosan-ascorbic acid@NIFE (CTAS@NIFE) catalyst for 70 mg·L−1 MG. The quenching of the photocatalytic efficiency from 98% to 64% in the presence of isopropyl alcohol (IPA) suggested the involvement of hydroxy (•OH) radicals in the mineralization process of MG. The high regression coefficients (R2) of 0.99 for 35, 55, and 70 mg·L−1 MG indicated the sonophotocatalysis of MG by CTAS@NIFE was best defined by a pseudo first-order kinetic model. The mechanism involves the adsorption of MG on the catalyst surface in the first step and thereby mineralization of the MG by the generated hydroxyl radicals (•OH) under the influence of visible radiation coupled with 6.34 W·mL−1 ultrasonic power. In the present study the application of photodegradation process with sonochemistry results in 99% of MG mineralization without effecting the material structure unlike happens in the case adsorption process. So, the secondary pollution (generally happens in case of adsorption) can be avoided by reusing the spent material for another application instead of disposing it. Thus, the ecofriendly synthesis protocol, ease in design of experimentation like use of solar irradiation instead of electric power lamps, reusability and high efficiency of the material suggested the study to be potentially economical for industrial development at pilot scale towards wastewater remediation.

Sonophotocatalytic Degradation of Pollutants by ZnO‐Based Catalysts: A Review

AbstractSonophotocatalyticprocess (SPC) is the simultaneous use of ultraviolet radiation (UV), ultrasonic radiation (US), and semiconductor materials as photocatalysts and sonocatalysts for the generation of reactive oxygen species (ROS). These free radicals oxidize several pollutant molecules in various industrial wastewaters. The objective of this review was to compare the papers published on the sonophotocatalytic degradation of different pollutants in the presence of zinc oxide‐based particles. The elimination rate of contaminants in this process was compared with individual methods such as sonocatalysis and photocatalysis. The experimental conditions, including the catalyst dosage, the pollutant concentration, the radiation power, the applied frequency, the initial pH, and the reaction time were further investigated. ZnO nanoparticles are well‐known as semiconductor materials with good sonophotocatalytic activity. In general, sonophotocatalysis is emerging as one of the most efficient treatment techniques for degrading the recalcitrant pollutants in the aqueous medium. It is expected that these technologies result in more progressive research with the most degradation efficiency.

Ce/Eu redox couple functionalized HKUST-1 MOF insight to sono-photodegradation of malathion

The Ce/Eu redox pair-functionalized HKUST-1 MOF, as an innovative environmentally friendly and recyclable sono-photocatalyst, was hydrothermally mixed and fully characterized by XRD, PL, EIS, FE-SEM, EDS, Mott-Schottky, chronoamperometry, and DRS techniques. The obtained chemical and optical characteristics of the n-type Ce/Eu-HKUST-1 MOF showed that the transfer of additional 4f orbital electrons in the Ce/Eu redox pair improves the sono-photocatalytic activity. The performance of Ce/Eu-HKUST-1 MOF for the sono-photodegradation of Malathion (MA) was evaluated in the aqueous media in the simultaneous presence of blue light and ultrasonic irradiation. The optimization of the process was cross-examined using the response surface methodology as a function of the MA concentration (15–35 mg·L−1), Ce/Eu-HKUST-1 mass (10–30 mg), pH (4−12), and ultrasonic wave irradiation duration (10–30 min). The maximum sono-photocatalytic degradation capacity was found to be 99.99% under the optimum conditions set as 25 mg·L−1, 20 mg, 8, and 25 min for the concentration of Malathion, photocatalyst mass, pH, and irradiation duration, respectively. These findings were attributed to the suppression of electron-hole pair recombination, increased life-time of charge carriers, enhanced visible light absorption, and prominent proportion of hydroxyl and peroxide radicals formed.

Sonolytic, sonocatalytic and sonophotocatalytic degradation of a methyl violet 2B using iron-based catalyst

The degradation of methyl violet 2B was efficiently carried out using sonolytic and sonophotocatalytic processes, FePO4 is a heterogeneous catalyst which has already shown its efficiency for the photocatalytic degradation of the earlier mentioned dye was used as a catalyst for the sonolytic process under a constant frequency of 500 kHz, effect of the parameters: pH, catalyst concentration ultrasonic intensity and dye concentration were also studied. The results show that a better degradation occurred under acidic pH (pH 3) with 1 g/L of the catalyst and an ultrasonic power P = 80 W. To further optimize the degradation process, ultrasound was coupled with UV radiation (λ = 254 nm), the dye degradation was improved from 68% using the sonolysis process to 100% using the sonophotocatalytic process with FePO4 as heterogeneous catalyst. Finally, degradation byproducts formed under optimized conditions were identified.

Synergic effect of Cu2O/MoS2/rGO for the sonophotocatalytic degradation of tetracycline and ciprofloxacin antibiotics

A ternary Cu2O/MoS2/rGO (Cu2MG) composite, synthesized by cost-efficient and eco-friendly microwave method, is potentially used for the sonophotocatalytic (visible light and ultrasonic irradiation) degradation of antibiotics namely tetracycline and ciprofloxacin. SEM and TEM observations reveal that the spherical Cu2O nanoparticles are decorated with MoS2 and rGO layered sheets. Furthermore, the incorporation of MoS2/rGO binary composite to Cu2O nanoparticles results in the reduction in fast electron-hole recombination and improve charge carrier ability of Cu2MG composite as confirmed by PL analysis. The Cu2MG composite demonstrates the synergic sonophotocatalytic degradation of Tetracycline (20 mg/L) and Ciprofloxacin (10 mg/L) antibiotics with high efficiency of 100% and 94% within a short duration of 10 min and 75 min, respectively. The kinetics study indicates that the degradation process obeys a pseudo-first order reaction with a rate constant as Ksonophotocatalytic > Kphotocatalytic > Ksonocatalytic. The high synergic value of 3.83 and 1.71 has been achieved for the degradation of TC and CIP antibiotics, respectively. The synergic effect of degradation is owing to the spontaneous production of OH˙ and ˙O2− radicals favoring free electrons to actively participate in the degradation process. This research work proves that the as-fabricated ternary Cu2MG nanocomposite is an efficient candidate for the degradation of antibiotics for better environmental protection.

Enhanced sonophotocatalytic degradation of paracetamol in the presence of Fe-doped TiO2 nanoparticles and H2O2

The presence of pharmaceutical compounds, particularly, paracetamol in water is of significant environmental concern due to their undesirable effects on aquatic organisms and poor biodegradability. The present work investigated the efficient degradation of paracetamol in water using sonophotocatalytic process in the presence of iron (Fe)-doped titanium dioxide (TiO2) nanoparticles. The effects of Fe doping into TiO2 and calcination temperatures were investigated using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, nitrogen adsorption–desorption analysis and X-ray photoelectron spectroscopy. It was discovered that 3 wt% Fe dopants into TiO2 nanoparticles with suitable calcination temperature at 600 °C could improve the sonophotocatalytic activity remarkably toward the degradation of paracetamol. The degradation efficiency of 100% was achieved under optimal experimental conditions, namely 5 mg/L initial paracetamol, 1 g/L 3 wt% Fe-doped TiO2-600, solution pH of 5, 0.5 mM of hydrogen peroxide (H2O2) after 30-min ultrasonic power of 296 W, ultrasonic frequency of 50 kHz and ultraviolet wavelength of 302 nm. These findings are crucial for designing Fe-doped TiO2 nanoparticles with high catalytic performance for the degradation of paracetamol and appeared as an alternative solution to treat pharmaceutical compounds effectively.

Sonophotocatalytic degradation of fast green in aqueous phase using undoped and nitrogen doped ZnO

Sonophotocatalytic degradation of fast green in aqueous phase using undoped and nitrogen doped ZnO

Sonophotocatalytic degradation of lignin: Production of valuable chemicals and kinetic analysis

Lignin, a key by-product of paper and pulp industry, and second-generation bioethanol refinery, is a potential source of platform chemicals due to its aromatic-rich structure. This study aims to demonstrate the synergism achieved by combining photocatalysis with ultrasound to depolymerize lignin into low molecular weight compounds. Sonophotocatalysis of lignin in alkaline aqueous medium using commercial TiO2 catalyst resulted in higher rate of degradation of lignin compared to photocatalysis. The increase in ultrasound frequency from 58 kHz to 58 + 132 kHz resulted in four-fold increase in lignin degradation rate. Upto 93 % degradation of lignin was achieved within 180 min via sonophotocatalysis. The molecular weight distribution of lignin was monitored using gel permeation chromatography to determine the change in number average and weight average molecular weights with time. At 2 g L−1 of TiO2 loading, 58 + 132 kHz ultrasound frequency, and initial lignin concentration of 100 mg L−1, the rate constant of lignin depolymerization, determined using the continuous distribution kinetics model with random scission, was 2.5 × 10-6 min−1 for sonophotocatalysis, while it was 0.93 × 10-6 min−1 for photocatalysis. The products obtained from sonophotocatalysis of lignin were 3,4-dihydroxy benzaldehyde, cinnamyl alcohol, 4-methyl-3-hexanone and succinic acid. The total yield of products from sonophotocatalysis of lignin was higher compared to that from photocatalysis. Overall, sonophotocatalysis is demonstrated to be a promising technique to degrade lignin and convert it to valuable chemicals.

Photocatalytic and sonophotocatalytic degradation of rhodamine B by nano-sized La2Ti2O7 oxides synthesized with sol-gel method

Nano-sized La2Ti2O7 oxides were synthesized by sol-gel route. The photocatalytic properties of the Rhodamine B degradation on this photocatalyst were studied as a function of crystallite size, dye concentration, catalyst loading, temperature and intensity of UV light flux. The photocatalytic results as well as the microstructural analysis, carried out by X-ray Diffraction and Transmission Electron Microscopy, revealed a strong correlation between the apparent rate constant and the crystallite size/degree of crystallinity of the photocatalyst. Temperature studies have shown optimum photocatalysis at 40 °C. Measurements of the zeta potential as a function of pH made it possible to determine the point of zero charge of the photocatalyst at pH = 8 and to understand the influence of pH on the degradation of cationic or anionic pollutants. Finally, the sonophotocatalytic process was studied showing a noticeable improvement in the apparent rate constant, multiplied by a factor of ∼1.7 compared to photocatalysis alone. The synergistic effect was quantified via measurements in sonocatalysis alone and then coupled to UV irradiation. This synergistic effect is about 23 % in the case of degradation of Rhodamine B on La2Ti2O7 oxides synthesized at 1000 °C.